Multi-stage sweetening process employing an alkaline hypochlorite solution



Dec. 1, 1959 GASOLINE FEED T. T. DAVIES EI'AL MULTI-STAGE SWEETENING PROCESS EMPLOYING AN ALKALINE HYPOCHLORITE SOLUTION Filed Aug. 6, 1956 {SOUR GASOLINVE BY-PASS SODIUM HYDROXIDE I SOLUTION V V I I HYPOCHLORITE RUNDOWN 3 MIXING TANK TANK SODIUM \37 5I 52 I HYPOCHLORITE I SOLUTION FINISHED I I GASOLINE SODIUM HYDROXIDE SOLUTION INVENTORS THOMAS T. DAVIES DAVID G. ROBERTS BY 4m Wm THEI ATTORNEY United States Patent MULTI-STAGE SWEETENING PROCESS EMPLOY- ING AN ALKALINE HYPOCHLORITE SOLUTION Thomas T. Davies and David G. Roberts, Heysham, England, assignors to Shell Development Company, New York, N.Y., a corporation of Delaware Application August 6, 1956, Serial No. 602,198 I Claims priority, application Great Britain August 10, 1955 6 Claims. (Cl. 208-190) This invention relates to the treatment of hydrocarbon oils and particularly to the sweetening or removal of mercaptans therefrom.

It is known to refine hydrocarbon oil distillates to remove sulfur compounds, such as mercaptans (including aliphatic and aromatic mercaptans), therefrom by subjecting the hydrocarbon oil to treatment with an alkali, for example, a solution of caustic soda, and then to an oxidizing treatment with a solution of an alkali metal hypochorite, for example, sodium hypochlorite. It is also known to subject the resulting hydrocarbon oil to treatment with an aqueous solution of a caustic alkali to reduce further the sulfur content thereof. Dependent upon the conditions under which such refining is carried out, for example, the alkalinity of the hypochlorite solution which is employed, mercaptans may be oxidized to oil-soluble noncorrosive sulfur-containing compounds, e.g., disulfides. Sweetened hydrocarbon distillate oils may thus be obtained which nevertheless possess a relatively high sulfur content.

When the hydrocarbon oil distillates are under-treated with the hypochlorite, that is, treated with insufficient hypochlorite to react under the employed reaction conditions with all of the mercaptans which are present, it is found that only a fraction of the quantity of the mercaptans which are originally present in the hydrocarbon oil, for example, one-half, have reacted, notwithstanding the fact that the amount of hypochlorite employed is in excess of that amount theoretically required for com plete reaction. It is therefore generally necessary in conventional hypochlorite treating processes to use far more than the theoretical, or stoichiometric, amount of hypochlorite solution in order to insure a doctor sweet product.

It is the principal object of the present invention to provide an improved process for the sweetening of hydrocarbon distillate oils by the use of hypochlorite solu tions. A more particular object is to provide such a process wherein the amount of hypochlorite solution consumed is reduced. Other objects will be apparent in the description of the invention.

It has now been discovered that mercaptans which are present in hydrocarbon distillate oils may be either re moved therefrom, that is, be converted into compounds which are extracted or be converted into comparatively harmless sulfur-containing compounds, for example, disulfides, in an especially economical manner byv subjecting the oils to at least two separate treatments with solutions of hypochlorite, the oils being under-treated with hypochlorite during each hypochlorite treatment except the final hypochlorite treatment, and subjecting the oils to treatment with aqueous caustic alkali solutions between eachhypochlorite treatment and also after the final hypochlorite treatment. It has been found that considerable economies in the consumption of hypochlorite are ob tained when such multi-stage treatment with hypochlorite is employed. No interaction should be allowed to occur Patented Dec. 1, 1959 between the fresh hypochlorite which is employed in the second or any subsequent hypochlorite treatment and the spent aqueous phase which is obtained from the preceding hypochlorite treatment, since such interaction has been found to result in ineffectual use and consequently waste of the hypochlorite which is employed. The spent, or partially spent, hypochlorite solutions are therefore separated from the hydrocarbon oil distillate at the conclusion of each of the treatments thereof with hypo chlorite, and each resulting hydrocarbon oil is washed with aqueous alkali solution. By means of this treatment with caustic alkali solution, various acidic materials which are present in the oils are removed. For example, alkyl 'sulfenyl chlorides formed in the hydrocarbon oil during the treatment thereof with hypochlorite, are by drolyzed to alkyl sulfenates, pass into the aqueous phase and are removed.

In the conventional processes of hypochlorite treating, whether single or multistage, much of the sulfur contained in the oil is converted into higher oxidating forms such as sulfonyl chloride (RSO Cl). By the use of a less-than-sutficient amount of hypochlorite solution in each of two or more stages with intermediate alkali washing steps according to the invention, this conversion, which of course consumes hypochlorite, will take place to a lesser extent, for example, to sulfenyl chlorides (RSCl) instead of to sulfonyl chlorides. The result is that the sulfur removed from the system, via both the spent hypochlorite solution from the first stage and the alkali solutions used to wash the oil after each hypochlorite treatment stage, will leave in an oxidation state lower than in conventional processes, thus elfecting an overall reduction in hypochlorite consumption.

It has been found that this invention enables hydrocarbon oil distillates to be sweetened by means of quantities of hypochlorite which are far less than the quantities thereof required by conventional sweetening processes. For example, sour gasolines may be sweetened by the process of this invention with quantities of hypo ch-lorite which are in the order of 1.5 to 2 theories. More over, the present process gives rise to hydrocarbon oil distillates which possess satisfactory acid values.

The present invention provides a process for sweetening a hydrocarbon oil distillate containing mercaptans but substantially no hydrogen sulfide by a two-stage treatment, each stage involving the successive application and separation of aqueous alkali metal or alkaline earth metal, preferably sodium or calcium, hypochlorite solution and aqueous caustic alkali solution, wherein the said hypochlorite solution is applied in the first stage in amounts between 0.5 and 2.0 theories based on the mercaptans present in the said distillate and is applied in the second stage in such amount as will ensure that the combined total used in the two stages is between 1.3 and 3.0 theories based on the mercaptans originally present in the said distillate.

The hydrocarbon oil distillate obtained from the sec- 0nd stage may be subjected to one or more further treatments with aqueous alkali metal or alkaline earth metal hypochlorite solution and/ or aqueous caustic alkali solution.

Throughout this specification and the claims hereinafter appearing, the term theory applied to alkali metal or alkaline earth metal hypochlorite solutions in connection with hydrocarbon oil distillates containing mercaptans is that amount of the hypochlorite solution employed which is theoretically required to oxidize the mercaptans present in the hydrocarbon oil distillate to' 2 Rea anci RSsRiNaCl-j-H O In cases where the mercaptan content of the particular hydrocarbon oil distillate which is to be subjected to the present process is not known, the mercaptan content thereof may be determined by any known method.

Before the hydrocarbon oil distillate is treated with the aqueous alkali metal or alkaline earth metal hypochlorite solution in the said first stage, it may be subjected to a preliminary treatment with an aqueous solution, for example, an aqueous alcoholic solution, of an alkaline material. Alkali metal and alkaline earth metal hydroxides are suitable alkaline materials. Such preliminary treatment removes certain sulfur compounds, for example, hydrogen sulfide, which may be present in the oil and removes therefrom materials which have an acid reaction. The said removal of materials having an acid reaction reduces the decomposition of the hypochlorite during the subsequent reaction of the oil with hypochlorite and tends the prevent the formation of chlorinated derivatives of petroleum hydrocarbons in this subsequent reaction. The said preliminary treatment may be effected with aqueous solutions containing up to 25% and preferably from 10% to 20% by weight of alkali, e.g., sodium hydroxide. The two liquids are generally brought into intimate contact, and the contact time which is employed can vary over a wide range. However, as in the case of all liquid contacting steps herein disclosed, the optimum time of contact is best determined by practical tests carried out upon the particular hydrocarbon oil to be treated. The temperature which is employed is generally between C. and 50 C., and ambient temperatures are generally very satisfactory.

The concentration of the alkali metal or alkaline earth metal hypochlorite solutions used in the two or more treatments of the hydrocarbon oil distillate may vary over a wide range. Typical hypochlorite solutions which may be employed are those between 0.05 N and 3.0 N with respect to hypochloride. The aqueous hypochlorite solutions may contain other materials which promote the desired oxidation reactions, which assist the removal of sulfur compounds or oxidized sulfur compounds from the hydrocarbon oil distillate, or which inhibit the decomposition of the hypochlorite in undesired side reactions such as chlorination of the hydrocarbon oil distillate. For example, the hypochlorite solutions employed may contain free alkali, for example, alkali metal or alkaline earth metal hydroxides, preferably sodium or calcium hydroxide. Typical percentages of such hydroxides which may be present in the hypochlorite solutions range from 0.05% to 1.0% by weight, and since hypochlorite solutions which contain no free alkali are particularly corrosive towards apparatus constructed of metals such as mild steel, it is desirable, in those cases where such apparatus is employed, for the hypochlorite solutions to be approximately 0.2 N with respect to alkali metal hydroxide in order to inhibit this corrosion. ferred that the hypochlorite solution used in the first stage contain no more than about 0.5% by weight alkali metal hydroxide because the process is most advantageous economically when the used hypochlorite solution from the first stage is discarded. Sodium or calcium chloride may be present in the hypochlorite solutions employed.

The hydrocarbon oil distillate and the said hypochlorite solutions are generally brought into intimate contact. The time of contact may vary over a wide range, and as stated previously, the optimum time of contact is best determined by practical tests carried out upon the particular hydrocarbon ,oil to be treated. In general, the time of contact in the first stage hypochlorite treatment should be suflicient to substantially reduce all of the hypochlorite in. the treating solution, and the time of contact in the second stage should be sufficient to produce a doctor sweet product. If desired, however, the time of contact in the second hypochlorite treatment can be less than this, but since the product will not then be doctor sweet, an additional finishing treatment will It is pre 4 be desirable. The temperature which is employed is generally between 0 C. and C. For example, ambient temperatures generally give highly satisfactory results.

The quantity of the hypochlorite solution which is contacted with the hydrocarbon oil distillate in the first stage may be between 0.5 and 2.0 theories, and preferably between 0.8 and 1.6 theories, for example, about one theory, based on the mercaptan content of the distillate entering the first stage.

After the spent hypochlorite solution has been separated from the hypochlorite-treated oil, the resulting oil has been treated wth an aqueous caustic alkali solution and the spent or partially spent caustic alkali solution has been separated therefrom, the oil so produced is treated in the second hypochlorite stage with an amount of aqueous alkali metal or alkaline earth metal hypochlorite solution such that the total amount of hypochlorite which is contacted with the hydrocarbon distillate in both stages is from about 1.3 theories to about 3.0 theories, preferably from about 1.4 to about 2.4 theories, for example, about 2.0 theories, based on the mercaptan content of the hydrocarbon oil distillate entering the first stage hypochlorite treatment.

The aqueous caustic alkali solutions which are brought into contact with the hydrocarbon oil distillate after the oil has been brought into contact with each hypochlorite solution, may contain water soluble alcohols. The concentration of alkali metal hydroxide in the caustic alkali solutions which are employed may vary over a wide range. The solutions preferably contain from 6% to 20% by weight of alkali metal hydroxide, but may be used until the alkali metal hydroxide contained therein is spent. The oil and the caustic alkali solution are generally brought into intimate contact, and the time of contact may vary over a wide range. The temperature which is employed is generally between 0 C. and 50 C. For example, ambient temperatures are generally very satisfactory.

Alkali metal mercaptides, derived from either aliphatic or aromatic mercaptans, may be present with the caustic alkali solutions when the latter are reacted with the hypochlorite-treated hydrocarbon oil distillate obtained from the first and/or any subsequent hypochlorite treatment. Compounds which are formed during the treatment of the hydrocarbon oil distillates with hypochlorite and which render said distillates corrosive towards metals, for example, sulfenyl and sulfonyl chlorides, are reacted upon by the alkali metal mercaptides and are converted into comparatively non-corrosive compounds, such as oilsoluble disulfides, even at ambient temperatures. Although compounds such as alkyl sulfenyl chlorides possess an acid reaction, not all such acidic compounds formed in the present process are necessarily removed by subjecting the hypochlorite-treated hydrocarbon oil distillates to treatment with caustic alkali solutions. Such residual acidity may be very conveniently removed by the above-mentioned mercaptide treatment.

The mercaptides which are reacted with the hypochlorite-treated distillate may be added thereto as such or may be dissolved in a suitable solvent and added thereto. For example, the caustic alkali solution may contain the alkali metal mercaptides together with a suitable solutizer. Caustic alkali solutions which have been used for extracting mercaptans from a hydrocarbon oil may be employed.

Moreover, the treatment of the hypochlorite-treated oil with caustic alkali solutions may be carried out in the presence of a hydrocarbon oil which contains mercaptans in order that mercaptides are formed in situ and elfect the desired reaction. The latter hydrocarbon oil is preferably substantially free from hydrogen sulfide. It may be a mercaptan-containing oil derived from the same source or from a different source as that of the original hydrocarbon oil distillate which is subjected to treatment, for example, the said hydrocarbon oil distillate may be anaphtha possessing a boiling range-of 80C. to 240 C. obtained by the distillation of a crude petroleum oil, and the said mercaptan containing oil may be a gasoline possessing a final boiling point of 80 C. which is obtained by distillation of the same or another crude petroleum oil. An especially advantageous method of supplying the mercaptide is to split the sour distillate available for the first hypochlorite stage into first and second streams, with the first stream being treated in the first and second hypochlorite stages, with intermediate casutic treatment as described above, and the second stream being mixed with the distillate from the second hypochlorite stage and this combined stream then being contacted with caustic. The quantity of mercaptides which is employed in this embodiment of the invention is preferably sufiicient to remove corrosive compounds from the hydrocarbon oil distillate to such an extent that theoil has an acid number, calculated as milligrams of potassium hydroxide required to neutralize 1 gram of the oil, 0.1 or less, and to produce a sweet hydrocarbon oil distillate. This amount is readily determined in practice and is generally from about 5 to about 100 mol percent, more especially, from about to 30 mol percent, based on the mercaptans present in the distillate entering the first stage hypochlorite treatment.

' The reaction between the hypochlorite-treated oil, the caustic alkali solution and the mercaptan-containing oil is preferably allowed to continue until the desired reaction is complete. The reaction may be carried out at ambient temperatures but higher or lower temperatures may be employed.

The hydrocarbon oil distillates obtained at any stage of the process of this invention may be subjected to further treating operations, for example, to filtration, to adsorption on a solid adsorbent or to washing with water,

before being passed to the next stage. In this invention,

the treatment of the hydrocarbon oil distillate with the aqueous solutions of alkali metal hydroxide, alkaline earth metal hydroxide, alkali metal hypochlorite or alkaline earth metal hypochlorite may be elfected by bringing the reactants into intimate contact with each other,

and may be effected by any known method. For example, the liquids which are to be brought into contact with each other may be stirred or agitated together, may be passed in co-current or in counter-current through appropriate conduits, may be fed into a rotating disc contactor or may be passed together through perforated discs, over baffle plates or through a propeller mixer or turbomixer. Moreover, one liquid may be injected or sprayed into the other in order that intimate mixing 'occurs. a

The separation from the hydrocarbon oil distillate of the aqueous layers comprising the spent or partially spent hydroxide or hypochlorite solutions, or the solutions obtained as a result of subjecting the oil to washing with water between such treatments, may be carried out by any known method. Thus, the oil and aqueous phases may be passed to settling tanks and the two phases may be separately removed therefrom. The partially spent solutions of alkali metal hydroxide may be employed in the preliminary washing treatment of further quantities of hydrocarbon oil distillate which are to be subjected to the process of this invention.

Suitable hydrocarbon oil distillates which may be treated by means of the present process include light hydrocarbon oil distillates which contain mercaptans but which are substantially free from hydrogen sulfide and which possess an end boiling point of less than 370 C.

The present'invention is particularly applicable to mercaptan-containing light petroleum hydrocarbon distillate fuels, for example, such fuels which may be employed as fuels in spark-ignitedinternal combustion engines, compression-ignition internal combustion engines, internal combustion turbine engines, heating apparatus and/or lighting apparatus. Thus they include gasolines, whether straight run, thermally reformed or' cracked, or catalytically reformed or cracked, or polymerized gasolines. This process may also be applied to fuels such as naphthas, aviation turbine fuels and kerosenes. It is especially applicable to hydrocarbon oils boiling in the gasoline and kerosene range, i.e., from about 30 C. to about 300 C.

The process of this invention may be carried out as a batch process or as a continuous process. One typical treating unit by means of which hydrocarbon oil distillates may be subjected to the present process is briefly described hereinafter with reference to the schematic flow diagram of the accompanying drawing, consisting of a single figure, and one particular method of carrying out the present process is exemplified with reference to the treatment of sour gasoline with solutions of sodium hypochlorite and sodium hydroxide in the said treating unit; One particular optional embodiment of this process, wherein the hypochlorite-treated hydrocarbon oil distil= late is treated with sour gasoline, 'isalso exemplified.

Sour gasoline is led through line 11 to a mixing tower or series of mixing towers 12 and is passed through the towers 12 co-currently with an aqueous solution of sodium hydroxide from line 13. The mixed aqueous and gasoline phases are then passed to a settling vessel 15, designated the first soda settler in the accompanying diagram, and are allowed to separate therein, the resulting aqueous layer comprising partially spent sodium hydroxide being recycled via line 13 to the mixing towers 12 while the resulting gasoline is passed via line 16 to the globe mixing valve 17 where it is intimately mixed with an aqueous solution of sodium hypochlorite from line 19. The mixture so obtained is passed to a settling vessel 21 wherein the spent hypochlorite is separated from the gasoline via line 22 and the hypochlorite-treated gasoline is passed via line 23 to a second globe mixing valve 24 together with aqueous sodium hydroxide solution from line 25. -The gasoline and the aqueous sodium hydroxide solutions are intimately mixed in both the mixing valve 24 and in a mixing tower or series of mixing towers 26 situated further downstream, and are then passed to a second soda settler 27 wherein an aqueous layer comprising partially spent sodium hydroxide solution and a gasoline layer are allowed to separate, the former layer being recycled to the last-mentioned mixing valve 24 via the line 25 and the latter layer being passed via line 28 to a further globe mixing valve 29 together with an aqueous solution of sodium hypochloride from line 31. The gasoline and the sodium hypochlorite solution are intimately mixed and then passed to the second hypochlorite settler 33 wherein the hypochlorite solution layer and the gasoline layer are allowed to separate. The partially spent hypo chlorite solution still contains sodium hypochlorite and is passed via line 34 to a hypochlorite mixing tank 37 wherein sodium hypochlorite solution suitable for react ing with the gasoline in globe mixing valves 17 and 29 is prepared by diluting a concentrated aqueous solution of sodium hypochlorite, for example, a 5.0 N solution thereof admitted via line 39, with fresh make-up water admitted via line 41. Free alkali, for example, sodium hydroxide solution, may be admitted via line 42 to the hypochlorite mixing tank 37.

The gasoline is drawn off from the second hypochlorite settler 33 via line 43 and may be mixed in the optional embodiment mentioned above with sour gasoline passed from the first mentioned soda settler via line 45 and valve 54. The resulting gasoline is passed via line 47 to a run down tank 51 and intimately mixed with an aqueous solution of sodium hydroxide contained therein. The sweetened gasoline so produced is then separated from the aqueous layer so obtained, is drawn off through line 52 and may then be blended and/or doped in preparation for use in an internal combustion engine.

The treating unit hereinabove describedis only one ex ample of the many possible, arrangements of equipment such as liquid phase mixing valves, mixing towers and settlers which may be employed to carry out the process of this invention. Thus, further mixing and settling stages may be employed to subject the gasoline to yet that number of milligrams of potassium hydroxide required to neutralize one gram of the distillate.

EXAMPLE I further treatments with hypochlorite and hydroxide solu- TWO 8011f Straight-r1111 gasohfles, two S0111 haphthas and tions. Also, sour gasoline from the first soda settler {W0 blends of 8011f Straight-11111 and Soul thermally-Temay be mixed with the gasoline from the first hypo formed gasolines, all Of which hydrocarbon Oil distillates chlorite settler so that sodium mercaptides will be present Were derived from predominantly Middle East sources, in the mixture passing through mixing valve 24, as menwere washed with an aqueous solution of caustic soda tioned before and further exemplified in the examples. and were then found to be substantially free from hydro- The hydrocarbon oil distillates which are sweetened 2 Sulfide and free Sulfur and t0 P055658 Properties 35 by the process of this invention may be subjected to afterset out m Table I heremafter pp A sample of treatments, such as water-washing, filtration, refluxing each sour hydrocarbon oil so obtained was subjected to over lime, or distillation. The sweetened oil may be the following tfeatmentin the O er hOWHi subjected to filtration through solid adsorbents such as 5 The sour hydrocarbon 011 was intimately mixed alumina, adsorbent earths or charcoal, for example, in W y based on the mefcaptan Content of the those cases where undesirable oxidized sulfur-containing 0f N sodlum hypochlorite Sohlhohcompounds of high molecular weight are yet present in The hydrocarbon 011 layer and the aqueous y the product, were separated and the spent sodium hypochlorite layer Moreover, the resulting distillates may be treated with was dlscafdei dopes such as organic compounds, organo-metallic com- The y q 011 was lllhmately mlxed Wllh pounds and/or inorganic compounds which confer specaushc Soda ncial properties thereon, particularly if the distillates are Th6 hydrocarbon 011 layer and the q l Caushc to be employed as fuels. For example, corrosion inhibilayer Wefe Separated and h latte? f y Was discardedtors, anti-knock agents, anti-icing agents, oxidation in- The hydrocarbon 011 w lnhmately mlXed With hibitors, for example, alkylphenols or aromatic amines, theory (based on Orlglhal mefc'aptan cfmtellt of gum inhibitors, detergents and scavenging agents may be the p Of N sodlhm hYPOChIOIItB 5011100!!- added to the resulting di till t (6) The hydrocarbon oil and aqueous layers were sep- Thus, compounds may be added to the distillates which arated and the Spent Sodium hypochloflte layer was (115- inhibit the power thereof to stain or corode metals such Cardedas iron or copper, for example, from 0.001% to 0.2% by h fehuhlhg hydrocarhoh 011 Was Wlth weight of substituted or unsubstituted aliphatic or cyclo- 10% of Its Welght 0f N cal-lshc Soda SOhltlOhaliphatic monocarboxylic acids which possess at least 12 Samples of the hydrocarbon oils which were obtained carbon atoms per molecule and a solubility in water which at each stage were analyzed, and the results obtained are Table I Sour oil de- Sour oil dc- Sour 011 de- Sour oil de- Sour 011 de- Sour oil derived from rived from rived from rived from rived from rived from blend of blend of straight-run straight-run straight-run straight-run straight-run straight-run gasoline gasoline naphtha naphtha and reformed and reformed gasoline gasoline A B C D E F Properties of sour hydrocarbon oil before treating:

Specific Gravity at /60 C 0. 648 0. 644 0. 7415 0. 7415 0. 7030 0. 7030 Dlsti1lation Initial boiling point, 0 26 29 104 95. 5 35 as recovery at C 67 64 143 143 141 141 Final boiling point, C 99. 5 160 170 Mercaptan content, percent w. mercaptan sulfur 0.029 0. 029 0. 025 0. 026 0.020 0. 023 Properties of oils subjected to process of invention:

After treatment with 1 theory of 1.0 N sodium hypochlorite solution- Mercaptan content, percent w. mercaptan sulfur 0.018 0. 020 0. 022 0. 020 0. 014 0. 016 After spent hypochlorite separated and oil washed with 10% volume 2 N caustic soda:

Mcrcaptan content, percent W. mercaptan sulfur 0.0052 0. 0042 0. 013 0. 013 0. 0056 0. 0064 After treatment with 0.5 theory of 0.10 N sodium hypochlorite:

Mercaptan content, percent w. mercaptau sulfur 0.0019 0. 0014 0. 011 0. 010 0. 0032 0. 0046 After spent hypochlorite separated and oil washed with 10% volume 2 N caustic soda:

Mercaptan content, percent w. mercaptan sulfur 0. 0004 0. 0004 Y 0. 009 0. 008 0. 0014 0.0023

does not exceed 0.1 gram per liter at 20 C., dicarboxylic 60 acids having at least 8 carbon atoms per molecule, or compounds such as morpholine.

Moreover, the hydrocarbon oil distillates which are produced by this process may be blended with other oils, such as hydrocarbon oils. For example, if the distillates which are produced are to be employed as fuels in spark-ignited internal combustion engines they may be blended with straight-run, thermally-cracked or catalytically-cracked gasolines, with aromatic hydrocarbons, such as benzene and toluene, or with volatile alcohols or others.

The present invention is illustrated by the following examples, wherein the mercaptan content of each of the various hydrocarbon oil distillates referred to is expressed as a percentage by weight of sulfur, and the term 75 acid va1ue applied to a hydrocarbon oil distillate is set out hereinafter in Table I. The final hydrocarbon oils which were obtained were doctor sweet.

For purposes of comparison, a further six samples of the same said sour hydrocarbon oils were subjected to a conventional refining treatment with solutions of sodium hypochlorite and sodium hydroxide.

This conventional treatment comprised subjecting each oil to a single stage treatment with a solution of sodium hypochlorite containing sodium hydroxide, which solution was 0.10 N with respect to sodium hypochlorite and 1.5 N with respect to sodium hydroxide. Each resulting oil was separated from the partially spent treating solution and was then washed with aqueous sodium hydroxide solution. 4.5 theories of sodium hypochlorite were required to sweeten the hydrocarbon oils by means of this conventional treatment.

9 EXAMPLE H A sour stream of mixed straight-run and thermallyreformed gasolines derived from Middle East sources was subjected to a preliminary washing treatment with an aqueous solution of caustic soda. The resulting stream of sour gasoline was substantially free from hydrogen sulfide and free sulfur but contained 0.28% by weight of sulfur in the form of mercaptans. This was subjected to the treatments enumerated in Examplel except that in step the gasoline was reacted with 0.7 theory, instead of 0.5 theory, of sodium hypochlorite, the gasoline being intimately mixed with 0.1 N sodium hypochlorite solution.

The final stream of gasoline which was obtained gave a negative doctor test.

EXAMPLE III A sour stream of mixed straight-run and thermallyreformed gasolines derived from Middle East sources which had been subjected to a preliminary washing with an aqueous solution of caustic soda, which was substantially free from hydrogen sulfide and free sulfur but which contained 0.027% by weight of sulfur in the form of mercaptans, was subjected to treatment with aqueous solutions of sodium hypochlorite and sodium hydroxide in accordance with the process of this invention. Apparatus of the type hereinbefore described and illustrated in the accompanying drawing was employed. The conditions under which the various operations were carried out and certain properties of the products obtained at various stages of the treatment are recorded in Table II below:

Table 11 Flow rates in tons (2240 pounds) per day:

Total sour gasoline flow 605 Sour gasoline through hypochlorite treaters 525 Sour gasoline through bypass 80 0.101 N sodium hypochlorite solution to mixing valve 17 0.101 N sodium hypochlorite solution to mixing valve 29 H I Average properties of various streams of treating solutions Sodium hypochlorite solutions to mixing valves 17 and 29 0.101 N NaOCl Hypochlorite in spent solution from first P hyipofhlorite tsetillerfifiiu guuTFn Nil er at y spen ypoe on e sou ion from second hypochlorite settler 0.046 N NaOCl Sodium hydroxide solution in the second soda settler 4.6 N NaOH Sodium hydroxide solution in the rundown tank 2.6 N NaOH Amount of sodium hypochlorite used based on mercaptan content of original gasoline passed through hypochlorite treaters:

Theories First-stage treatment with sodium hypochlorite 1.14

Second-stage treatment with sodium hypochlorite-.. 0.62

Mercaptan Average Properties of Various Content,

Gasoline Streams Percent W. Acidity Mercaptan Sulfur From first soda settler after preliminary washing 0. 027 From first hypochlorite settler 0.013 0.076 From second soda settler 0.007 0.001 From second hypochlorite settler 0.003 0.051 From rundown tank after soda wash but before blending with sour gasoline 0.002 0.033 From rundown tank after blending with sour gasoline and after soda wash 0. 0015 0.002

Thus, 1.76 theories of sodium hypochlorite, based on the mercaptan content of the gasoline which was passed through the hypochlorite treaters, i.e., 1.53 theories of sodium hypochlorite based on the mercaptan content of the total original gasoline which had been subjected to a preliminary washing with caustic soda and subsequently refined, were required to efiect this degree of refining.

For purposes of comparison, the same stream of gasoline which had been subjected to a preliminary washing with an aqueous solution of caustic soda and which contained 0.027% by weight of sulfur in the form of mercaptans, was subjected to the same conventionaLre- .1, 10 fining treatment as is specified in the last part of Example I for the comparative process. It was found, however, that 4.5 theories of sodium hypochlorite were required to efiect the same degree of refining as was obtained by the process of this invention.

EXAMPLE IV A sour gasoline stream comprising 50% of a straightrun gasoline and 50% of a thermally-reformed gasoline derived predominantly from Middle East sources was washed with an aqueous solution of caustic soda. The resulting sourgasoline was substantially free from hydrogen sulfide and free sulfur but contained 0.0242% by weight of sulfur in the form of mercaptans, and was subjected to treatment with aqueous solutions of sodium hypochlorite and sodium hydroxide in accordance with the process of this invention. The sodium hypochlorite solutions employed contained a small amount of free sodium hydroxide in order to minimize corrosion of the apparatus. Apparatus of the type hereinbefore described and illustrated in the accompanying drawing was employed. The stream was run for 24 days, and the condi# tions under which the various operations were carried out and certain properties of the products obtained at various stages of the treatment are set out in Table III below:

Table III Flow rates in tons (2240 pounds) per day:

Total sour gasoline fiow 560 Sour gasoline through hypochlorite treaters Sour gasoline through bypass line 45 Hypochlorite solution to first mixing valve 17 40 Hypochlorite solution to second mixing valve 29 78 Average properties of various streams of treating solutions Strong sodium hypochlorite solutions to mixin tank 37 5.25 NNaOCl Sodium ypochlorite solutions to m g valves 17 and 29 {0.106 NNaOCl 0.162 N NaOH Hypochlorrte in spent solution from first hypochlorite settler Nil Partially spent hypochlorite solution from second hypochlorite settler passed via line 34 to mixing tank 37 0.045 N NaOCl Sodium hydroxide solution in the second soda settler 2.5 NNaOH Sodium hydroxide solution in the rundown tank 2.0 NNaOH Amount of sodi urfn 1355651313555 fiifiis'e'd on mercaptan content of original gasoline passed through hypochlorite Thus, 2.33 theories of sodium hypochlorite, based on the mercaptan content of the gasoline which was passed through the hypochlorite treaters, i.e., 2.12 theories of sodium hypochlorite based on the mercaptan content of the total original gasoline which had been subjected to a preliminary washing with caustic soda and subsequently refined, were required to effect this degree of refining.

For purposes of comparison, the same stream of gasoline which had been subjected to a preliminary washing with an aqueous solution of caustic soda and which contained 0.0242% by weight of sulfur in the form of mercaptans, was subjected to the same conventional refining treatment as is specified in the last part of Example I for the comparative process.

It was found that 4.7 theories of sodium hypochlorite, based on the mercaptan content of the total gasoline obtained as a result of the preliminary washing with caustic same mercaptan content as that of the final gasoline produced by the process of this invention.

EXAMPLE v The sour gasoline used in Example II, when treated exactly in accordance with the procedure set out in Example I but using 0.1 N calcium hypochlorite solution, instead of sodium hypochlorite solution in steps (1) and and in approximately equivalent amounts, gives a negative doctor test.

We claim as our invention:

1. A process of removing mercaptans from a hydrocarbon oil distillate comprising the steps: (1) contacting said distillate with from about 0.5 to about 2.0 theories of a 0.05 N to 3.0 N aqueous solution of a hypochlorite selected from the group consisting of sodium and calcium hypochlorite, and separating the distillate therefrom; (2) contacting the distillate from step (1) with an aqueous caustic alkali solution, and separating the distillate therefrom; (3) contacting the distillate from step (2) with an amount of 0.05 N to 3.0 N aqueous solution of said hypochlorite such that the total amount used in steps (1) and (3) is from about 1.3 to about 3.0 theories, and separating the distillate therefrom; and (4) contacting the distillate from step (3) with an aqueous caustic alkali solution.

2. A process of removing mercaptans from a hydrocarbon oil distillate boiling below about 370 C. comprising the steps: (1) contacting said distillate with from about 0.5 to about 2.0 theories of 0.05 N to 3.0 N aqueous sodium hypochlorite solution, and separating the distillate; (2) contacting the distillate from step (1) with an aqueous solution of sodium hydroxide, and separating the distilate; (3) contacting the distillate from step (2) with an amount of 0.05 N to 3.0 N aqueous sodium hypochlorite solution such that the total amount used in steps (1) and (3) is from about 1.3 to about 3.0 theories, and separating the distillate; and (4) contacting the distillate from step (3) with an aqueous solution of sodium hydroxide, and recovering the distillate having a reduced mercaptan content.

3. A process according to claim '1 wherein from about 0.8 to about 1.6 theories of the hypochlorite solution is used in step (1) and 'the'amount of hypochlorite solution used in step (3) is such that the total amount used in steps (1) and (3) is from about 1.4 to about 2.4 theories.

4. A process according to claim 2 wherein the aqueous solution of sodium hydroxide used in step (4) contains sodium mercaptides.

5. A process according to claim 2 wherein the sodium hypochlorite solution used in steps 1) and (3) contains from about 0.05 to about 1.0% by weight sodium hydroxide.

6. A process of removing mercaptans from a mercaptan-containing hydrocarbon oil distillate comprising (1) splitting the distillate into a first and a second stream of like compositions, the second stream being from about 5% to about of the first stream; (2) contacting the first stream with from about 0.5 to about 2.0 theories, based on the mercaptans in the first stream, of 0.05 N to 3.0 N aqueous sodium hypochlorite solution, and separating the first stream; (3) contacting the first stream from step (2) with an aqueous solution of sodium hydroxide, and separating the first stream; (4) contacting the first stream from step (3) with an amount of 0.05 N to 3.0 N aqueous sodium hypochlorite solution such that the total amount used in steps (2) and (4) is from about 1.3 to about 3.0 theories, based on the mercaptan content of the first stream entering step (2), and separating the first stream; (5) mixing the first stream from step (4) with the second stream from step (1); and (6) contacting the total stream from step (5) with an aqueous solution of sodium hydroxide, and recovering the distillate having a reduced mercaptan content.

References Cited in the file of this patent UNITED STATES PATENTS 1,999,041 Dunstan Apr. 23, 1935 2,717,856 Richards et al. Sept. 13, 1955 2,721,166 Earhart Oct. 18, 1955 2,766,182 Le Nobel et al. Oct. 9, 1956 

1. A PROCESS OF REMOVING MERCAPTANS FROM A HYDROCARBON OIL DISTILLATE COMPRISING THE STEPS: (1) CONTACTING SAID DISTILLATE WITH FROM ABOUT 0.5TO ABOUT 2.0 THEORIES OF A 0.05 N TO 3.0N AQUEOUS SOLUTION OF A HYPOCHLORINE SELECTED FROM THE GROUP CONSISTING OF SODIUM AND CALCIUM HYPOCHLORITE, AND SEPARATING THE DISTILLATE THEREFROM; (2) CONTACTING THE DISTILLATE FROM STEP (1) WITH AN AQUEOUS CAUSTIC ALKALI SOLUTION, AND SEPARATION THE DISTILLATE THEREFROM; (3) CONTACTING THE DISTILLATE FROM STEP (2) WITH AN AMOUNT OF 0.05 N TO 3.0 N AQUEOUS SOLUTION OF SAID HYPOCHLORITE SUCH THAT THE TOTAL AMOUNT USED IN STEPS (1) AND (3) IS FROM ABOUT 1.3 TO ABOUT 3.0 THEORIES, AND SEPARATING THE DISTILLATE THEREFROM; AND (4) CONTACTING THE DISTILLATE FROM STEP (3) WITH AN AQUEOUS CAUSTOC ALKALI SOLUTION. 